Astronomy Ch 5 HW
Why are the sources of cosmic rays difficult to locate?
Cosmic rays are charged particles, thus their paths are curved by magnetic fields, which masks the location of their source.
When telescopes in different locations work together, it is called which of the following?
interferometery
Which theoretical power of an optical telescope is determined by the diameter of the primary mirror or lens?
light-gathering power and resolving power
Which reason for building a large telescope applies only to radio telescopes?
long wavelength light
Which power of a telescope is the least important?
magnifying power
You see a telescope advertised as 200 power.
magnifying power
You see a telescope advertised as 200 power. What quality of a telescope is least important?
magnifying power.
Radio telescopes are often connected together to do interferometry. What is the primary problem overcome by radio interferometry?
poor resolving power
Which of the following lists has the types of electromagnetic radiation in order of decreasing wavelength from left to right?
radio, infrared, visible, ultraviolet, gamma-ray
Which of the lists below has the colors of visible light in order of increasing frequency from left to right?
red, yellow, green, blue
Which power of a large ground-based optical telescope is severely limited by Earth's atmosphere on a cloudless night?
resolving power
Which power of a telescope might be expressed as "0.5 seconds of arc"?
resolving power
Resolving Power of a Telescope II. If the resolving power of a telescope is 1 arc second, do two stars 1.5 arc seconds apart look like separate points of light or a single blurred image at the wavelength of 550 nm, assuming the lenses and seeing are good?
separate points of light
Which is not a type of electromagnetic wave?
sound
Astronomers are both hindered and assisted by chromatic aberration. In which device is chromatic aberration a big problem for astronomers?
the primary lenses of refracting telescopes
Why must far-infrared telescopes be cooled to a low temperature?
to reduce interfering heat radiation emitted by the telescope
If a telescope has a resolving power of 0.1 sec of arc, what do two stars 1.5 seconds of arc apart look like through this telescope?
two separate blobs of light
In this figure you can see that different wavelengths of light are refracted (bent) by different amounts. Which wavelengths are bent by the greatest amount?
Short wavelengths
Based on the instruments used by astronomers to analyze light, select all of the correct statements from the following list.
Spectral lines observed from astronomical objects tell astronomers what atoms are present. Prisms and gratings spread light out into its spectrum by bending the direction of different wavelengths of light in different directions. Photography in astronomy has mostly been replaced by CCD imaging. In modern spectrographs, gratings have replaced prisms.
The primary mirror of telescope A has a diameter of 20 cm, and telescope B has a diameter of 100 cm. How do the light-gathering powers of these two telescopes compare?
Telescope B has 25 times the light-gathering power of telescope A.
A Sense of Proportion: The wavelength of visible light is about 5500 times longer than the wavelength of x-rays. If you represent the wavelenth of an x-ray photon by a line 1 inch long, how long a line (in feet) must you draw to represent the wavelength of visible light? The wavelength of AM radio waves is roughly times longer than the wavelength of visible light. How long a line (in Astronomical Units) must you add to your diagram to represent the wavelength of AM radio waves?
- 458 Feet -9 AU
Which is true of chromatic aberration?
All of these choices are true. It affects telescopes. It creates fringes around an image. It is caused by refraction.
Light Energy. Visual light can have a wavelength of 400 nm for violet light or 700 nm for red light. Which of the two wavelengths (violet or red) has the greater amount of energy carried by the photon? - Is this wavelength comparatively short or long? - Is the frequency comparatively high or low? - Based on your answers, which side of the electromagnetic spectrum has more energy, the red side or the violet side? -
-Violet - Short - High - Violet
A Sense of Proportion: Conventional telescopes in orbit looking down at Earth can resolve objects as small as 8 feet in diameter so they can image individual cars on highways. When astronomers link optical telescopes together to make an interferometer, they can resolve objects about 250 times smaller. How small a detail could such a telescope image if it could look down at Earth from orbit?
0.384
Compare the light-gathering powers of one of the Keck telescopes (10 m in diameter) and a 0.07-m telescope. ________
20400
A spy satellite orbiting 500 km above Earth is supposedly capable of counting individual people in a crowd. Roughly what minimum-diameter telescope must the satellite carry? (Hint: Use the small-angle formula. Assume that a human is about 0.5 m from shoulder to shoulder.)
56 cm
How does the light-gathering power of a 6-m telescope compare with that of the human eye? (Hint: Assume that the pupil of your eye can open to about 0.008 m.) ________
560000
Why are there arrays of many more than two radio telescopes working together?
Additional telescopes in between the two farthest-separated telescopes increases the gathering power and resolving power of the effective telescope
You see a telescope advertised as 200 power. What qualities of a telescope are important to you as a potential buyer?
All of the these choices are important. a solid mounting quality of the optics diameter of the objective
Why have no large refracting telescopes been built since 1900?
All of these choices are correct . Refracting telescopes suffer from chromatic aberration. Making large glass lenses without interior defects is difficult. Refracting telescopes have several surfaces to shape and polish. Large glass lenses are more difficult to support than large mirrors.
What advantage do the builders of large telescopes today have over the previous generation of telescope builders?
All of these choices are correct. Large mirrors can now be made thinner and lighter than before. Tracking celestial objects today is computer controlled and can take advantage of simpler, stronger mounts. High-speed computing today can be used to reduce the effect of Earth's atmosphere. Tracking celestial objects today is computer controlled and can take advantage of simpler, stronger mounts and high-speed computing today can be used to reduce the effect of Earth's atmosphere.
What is a disadvantage of radio telescopes compared to optical telescopes?
All of these choices are correct. Radio photons have power energy, thus radio waves have low intensity. interference from nearby sources of radio waves poor resolving power Radio photons have lower energy, thus radio waves have low intensity and interference from nearby sources of radio waves.
What do the newer light-sensitive electronic CCD chips do better than the older photographic plates coated with light-sensitive chemicals?
All of these choices are correct. They have a greater sensitivity to light. They can detect both bright and dim objects in a single exposure. Photometry can be done with the CCD images The CCD images are easier to manipulate.
Which is something that all electromagnetic waves have in common?
All of these choices are correct. amount of energy they deliver frequency speed wavelength
What device could replace photographic plates in astronomy?
CCD
What is the cause of the distortion shown in the image on the left?
Earth's Atmosphere
A Sense of Proportion: Arrange the following photons in order of increasing wavelength:
Gamma ray, X-ray, Blue, Green, Yellow, Red
Which is better, the resolving power of an 8-m telescope on Earth without adaptive optics or that of the 2.5-m Hubble Space Telescope?
Hubble Space Telescope
Why must telescopes observing in the far infrared be cooled to low temperatures?
If not cooled, the telescope will give off more infrared radiation than what it is observing
Which could be a disadvantage of a thin or "floppy" telescope mirror?
It tends to sag under its own weight
Which is not a reason to fail to classify sound as an electromagnetic wave?
It cannot travel in a vacuum.
Which is true about a prism spectrograph?
It divides light into the individual components of its spectrum.
If two radio telescopes work together, which of the following is the size of the effective telescope?
It is equal to the distance between the telescopes.
Based on the relationships among light, electromagnetic radiation, and photons, select all of the correct statements from the following list.
Light can act both as a wave and a particle. All electromagnetic waves travel at the speed of light. High frequency photons carry more energy than long wavelength photons. A photon is a particle of light.
You see a telescope advertised as 200 power
Maybe, depending on other factors, like the diameter of the objective or the quality of the optics
Based on astronomy from space-based telescopes, select all of the correct statements from the following list.
Most types of electromagnetic waves are not visible to ground-based telescopes. The Chandra and Spitzer telescopes are all in space.
If you were to make a telescope using the two lenses shown here, which lens should you use for the primary (objective) and which for the eyepiece?
One uses top lens for the primary and bottom lens for the eyepiece.
Based on the different types of optical telescopes and their relative strengths and weaknesses, select all of the correct statements from the following list.
Recently built modern telescopes are reflectors.
A Sense of Proportion: Arrange the following photons in order of increasing energy:
Red, Yellow, Green, Blue, X-Ray, Gamma ray
In which device do astronomers take advantage of chromatic aberration?
The Prism
Why are near-infrared telescopes located on mountaintops and ultraviolet telescopes in Earth's orbit?
The primary infrared blocker, water vapor, is mostly in the lower atmosphere and the primary ultraviolet blocker, ozone, is located high in the atmosphere, far above mountaintops.
Of the two telescopes shown here, which will allow you to see dimmer objects?
The telescope on the left.
Telescope mirrors have a reflective coating on their front surface as shown here. What major problem would be introduced if the reflective coating were beneath the glass surface?
There would be some chromatic aberration
What do large diameter, gently curved convex (thicker in the middle) lenses and large diameter gently curved concave (thinner in the middle) mirrors have in common?
They both have long focal lengths and can be used as primary light collectors for a telescope
What is the difference between chromatic aberration and a prism spectrograph?
They represent the same interaction between light and matter, but one is "good" and one is "bad."
Why do nocturnal animals usually have large pupils in their eyes?
To gather more light, so they can see better at night.
The visible part of the electromagnetic spectrum can be divided into seven color bands: red, orange, yellow, green, blue, indigo, and violet (from long to short wavelength). A single photon of which of these colors has the greatest amount of energy?
Violet
The entire electromagnetic spectrum can be divided into seven bands: radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray (from longest to shortest wavelength). To which of these two bands is Earth's atmosphere the most transparent?
Visible and Radio
How was the image on the left corrected to give the image on the right?
With adaptive optics
Most of Galileo's telescopes had objective lenses which were only about 2 cm in diameter. Theoretically, should he have been able to resolve two stars 14 seconds of arc apart? (Hint: resolving power in seconds of arc = 0.113/diametr of objective (in meters)
Yes, because the objective is sufficiently large.
With limited funds, which type of telescope would be your choice?
a reflector, because it is less expensive than the same size refractor, and can be made larger than a refractor
Why are telescopes in different locations working together especially desirable for radio telescopes?
because radio telescopes have such poor resolution
Why do radio telescopes have such poor resolution?
because radio waves have such a long wavelength
Which reason to build a large radio telescope also applies to optical telescopes?
better resolution
Which list has the colors of visible light in order of increasing wavelength from left to right?
blue, green, yellow, red
Which is the reason that radio telescopes are often put in valleys?
interference
The image below is an X-ray image of an exploded star. The colors in the image are
false colors that represent areas of different intensity within the image
Which of the different telescopes designed for the following specific types of electromagnetic waves has to be at the highest altitude from the surface of the Earth to be useful?
far UV to X-ray
Which type of telescope is more expensive?
for the same size objective, refractors
Which is better observed by an X-ray telescope than an infrared telescope?
hot gas trapped in galactic clusters
